The deployment of the proposed cloud-enabled HAPS system, as any traditional heterogeneous cloud-radio access network (HC-RAN), is subject to specific physical constraints, i.e., depending on the availability of communication resources and the limited level of coordination between the BSs [1]}. Generally speaking, resource allocation in interference networks is challenging due to the non-convexity of the majority of interference management problems; hence, the literature focuses on devising practical numerical solutions for optimizing HC-RANs. For instance, various techniques for local optimality have been proposed over the years with different considerations and limitations. For example, the authors in [2]} present a comprehensive overview of interference management techniques for cooperative multiple-input multiple-output (MIMO) systems, where several BSs within the same cell cooperate to serve users. The authors in [2]} highlight the constraints on such a network MIMO approach in terms of limited backhaul capacity, per-BS power consumption, and the need for decentralized processing; some of such challenges are further addressed in [4]}, [5]}.
